1. Field of the Invention
The present invention relates to the field of optical microscopes, and more particularly to optical microscopes used in the fabrication and packaging of semi-conductor devices.
2. Art Background
After the fabrication of an integrated circuit "chip", lead wires are bonded from the integrated circuit package which encapsulates the chip to conductive elements ("pads") on the circuit itself. Frequently, wire bonding is achieved by optically lining up the numerous pads on the periphery of the circuit chip with the lead wires, and then effectuating the actual bonding using techniques well known in the art. Various optical systems have been developed over the years to provide the bonding operator with a simultaneous image of the pads and leads. For example, in one system commonly used a video camera is coupled to a microscope thereby providing an image of the circuit with its associated conductive pads on a cathode ray tube (CRT) display. The operator, using the CRT image as a guide, lines up the leads with the conductive pads, and then completes the bonding process.
However, with the advent of very large scale integration (VLSI) technology, the size of the chip and the number of pads on a VLSI microelectronic device is significantly greater than previously found in the art. For example, it is anticipated that in the near future, integrated circuits with 200 to 300 pads and associated leads will be commonplace. Presently, wire lead bonding systems typically bond 1 mil leads to 4 mil-square pads, on 8 mil centers (See J. Lyman, "Packaging VLSI", Electronics, Dec. 29, 1981, Page 66). For VLSI chips larger than approximately 1/5 inch, with 2 mil pads on 4 mil (or smaller) centers, present video display systems are unable to adequately resolve each pad while displaying the entire chip, which is necessary in order to permit lead bonding. Accordingly, there exists a need for an optical display system which will permit the bonding of VLSI circuits, and which will permit standard video and CRT display systems to be used to align the conductive pads with the lead wires.
As will be disclosed below, the present invention provides a means whereby selected portions of an integrated circuit may be displayed to permit alignment of lead wires for bonding. As will be appreciated from the discussion which follows, the present invention is particularly suited for use with integrated circuits incorporating very large scale integration technology, although it may be used in numerous applications where only selected portions of one or more objects are to be viewed.